Blower unit



A. A. ATALLA 2,976,352

March 21, 1961 BLOWER UNIT 5 Shets-Sheet 1 24 FIG.4A zo j 14 Filed NOV.14, 1957 INVENTOR.

ANWAR A. ATALLA BY Wi'mcM/M'a A TTORNEVS March 21, 1961 Filed Nov. 14,1957 A. A. ATALLA 2,976,352

BLOWER UNIT 3 Sheets-Sheet 2 INVENTOR. ANWAR A. ATALLA BY TJZM 0M ATTORNEYS March 21, 1961 A. A. ATALLA BLOWER UNIT 3 Sheets-Sheet 3 FiledNov. 14, 1957 AIR FLOW C.F.M.

INVENTOR. ANWAR A. ATALLA BY W 5' m a ATTORNEYS BLOWER UNIT Anwar A.Ataila, Torrington, Conn, assignor to The Torrington ManufacturingCompany, Torrington, Conrn, a corporation of Connecticut Filed Nov. 14,1957, Ser. No. 626,537

22 Claims. (Cl.-2391li7) The invention relates to a blower unit adaptedfor use with warm air furnaces and with air conditioning installationsand otherwise, said unit being of the type that includes a housinghaving an air intake opening in one side wall and having a second wallparallel with said side wall and further having a discharge opening. Theunit also includes a motor located with its shaft concentric with theintake opening and the unit has an air impeller located within thehousing and driven by the motor and serving to draw air inwardly throughthe intake opening and to discharge said air through the dischargeopening. As shown and as frequently preferred, the housing has twoparallel side walls and has two opposite intake openings in said sidewalls. The motor is located within the housing and there are twoimpellers driven by the motor and serving to draw air inwardly and inopposite directions through said intake openings.

The general object of the invention is to provide a unit of the statedtype that is simple and compact and inexpensive, and that has favorablepower and performance characteristics through a wide range of operatingconditions.

A more specific object of the invention is to provide a unit having asubstantially flat power curve, the horsepower output of the motor andthe speed of the motor varying to only small extents as the dischargepressure the constructions disclosed, and that the drawings anddescription are not to be construed as defining or limiting the scope ofthe invention, the claims forming a part of this specification beingrelied upon for that purpose. In each of the illustrated embodiments ofthe invention, there are two impellers at two opposite intake openings,but it will be understood that the invention in its broader aspects isnot so limited.

Of the drawings:

Fig. l is a side view of a two-impeller blower unit embodying theinvention, certain parts being broken away to more clearly show otherparts.

Fig. 2 is a right end view of the blower unit with certain parts brokenaway and with other parts in vertical central section.

Fig. 3 is an enlarged fragmentary sectional view taken along the line3-3 of Fig. l.

Fig. 4 is a side view of one impeller with parts broken away to show thedetails of construction, this propeller being that shown at the left inFig. 2.

Fig. 4 is a fragmentary view similar to the upper left portion of Fig. 2and showing an alternative embodiment of the invention.

Fig. 5 is an enlarged fragmentary schematic view showice?- ing therelationship of one'impeller blade to the axis of rotation and to thecentral partition and to other parts.

Fig. 6 is a fragmentary view similar to the upper por' tion of Fig. 2and showing an alternative two-impeller unit embodying the invention.

Fig. 7 is a fragmentary side view showing a portion of one of theimpellers shown in Fig. 6.

Fig. 8 is a fragmentary view similar to the upper portion of Fig. 2 andshowing another alternative two-impeller unit embodying the invention; 7

Fig. 9 is an enlarged fragmentary view taken along the line 9-9 of Fig.l, but showing a detail of construction which is ordinarily used onlywith the alternative construction shown in Fig. 8. e

Fig. 10 is a chart showing representative performance characteristics ofa blower unit embodying the invention. Referring to the drawings andmore particularly to Figs. 1 to 5 thereof, the main housing of theblower unit is represented at '10, said housing preferably being formedof sheet metal. The shape of the housing can be \m'dely varied, but itis shown as being of the scroll or involute type. When the housing is ofthe last type, there is a longitudinal axis 12 and the housing has aperipheral wall 14'WhlCll conforms to a surface generated by moving aline approximately in an involute path about said axis 12. The housingis shown as having similar opposite parallel front and rear sidewalls'16 and 18. As shown, the peripheral wall 14 has opposite flanges2t? and 22 which engage the peripheral portions of the side walls 16 and18 and which are suitably connected therewith, as for instance, by spotwelding. When there are two side walls 16 and 18, they are provided withsimilar large intake openings which openings are concentric with theaxis 12. The housing has a relatively large peripheral discharge opening24. The opening 24 is shown as being rectangular and it is defined inpart by extended portions of the peripheral wall 14 and of the sidewalls 16 and 18 and is further defined by a fourth wall 26 at the bottomthereof, said wall 26 being'suitably connected with said sid walls andsaid peripheral wall. t

When there are two side walls such as 16 and 18,'two generallycylindrical shrouds 28 and 30 are fitted respectively within the intakeopenings in the side Walls, these.

shrouds being concentric with the axis 12. As shown in Figs. 1 to 5, thetwo side wall openings are of the same size and the two shrouds are ofthe same size. The major portions of the shrouds are cylindrical andsaid cylindrical portions are located to a major extent within thehousing, but they may also extend outside of the housing.

Said shrouds are suitably connected with the side walls,

and when they are partly outside of the housing they may be connected bymeans of circular angle rings 32 and 34.

The outer portions of the shrouds 28 and 30may be bell-- mouthed asshown.

When there are two side walls such as 16 and 18 and two shrouds such as28 and 30, a central panel or partition 36 is provided within thehousing midway between and parallel with the side walls, this partitionbeing formed of sheet metal and being suitably connected'with theperipheral wall 14, as for instance by means of a flange- Said partition36 extends nearly to the discharge. opening 24, but preferably has itsedge 40 spaced ininafter described motor and motor supportand the corre:

sponding one of said air impellers.

An electric motor 44 is provided with its drive shaft concentric withthe central axis and with a portion of its shaft projecting toward atleast one of the side walls 16 and 18. When there are two chambers and acentral partition 36, said partition has an opening 42 thereinconcentric with the axis 12 and the electric motor 44 is located at saidopening. The motor includes a casing, preferably cylindrical, and itincludes a drive shaft 46 having portions projecting at both ends of thecasing. Means is provided for supporting said motor on said partitionwith its center of gravity at the central plane of the partition. Themotor casing is symmetrically located in said partition opening 42 andthe portions of said shaft 46 are concentric with said central axis 12,said shaft portions projecting toward the planes of the housing sidewalls 16 and 18.

The supporting means for the motor preferably supports the motorresiliently, and it is shown as including a supporting ring or strap 48located within said opening 42, but preferably not closely fitting saidopening. When the supporting means supports the motor resiliently, thestrap 48 is preferably connected with the partition 36 by means of aplurality of resilient connections 50. As shown, there are three suchconnections equally spaced circumaxially and one of said connections isillustrated in detail in Fig. 3.

In each said resilient connection a rubber grommet 52 is fitted within ahole in the partition 36, said grommet having a central bushing 54therein. Preferably, in order to provide a larger bearing area for thegrommet 52, a small plate 56 is welded or otherwise secured to thepartition and has a hole for the grommet which has the same diameter asthat in the partition. At one side of the grommet 52 is a clip 58rigidly connected by welding or otherwise with the strap 48. At theopposite side of the grommet is a washer 60. A headed bolt 62 extendsthrough said bushing 54 and through holes in the clip and washer, and anut 64 on said bolt serves to firmly connect all of the last said partswith each other. By means of the three connections 50, 50 the strap 48is firmly but resiliently connected with the partition plate 36.

The casing of said motor 44 fits within the strap 48 so as to be heldthereby in the stated relationship with the panel or partition 36 andwith the housing. The supporting strap 48 is split and it has two spacedears 66, 66 as shown in Fig. l, the opening 42 having a notch 67 toreceive said ears. Bolts 68 extend through holes in the said ears, andby means of said bolts the ears 66, 66 can be drawn toward each other soas to firmly clamp the strap 48 against the periphery of the motorcasing. Thus the strap firmly engages the motor 44 and serves toresiliently support said motor.

A conducting cable 70 for supplying current to the motor 44 extendsupwardly through an insulating bushing in the lower portion of theperipheral housing wall 14 and then to themotor. As shown in Fig. 3, atleast one electrical connecting wire 72 is engaged by the head of acorresponding one of the bolts 62 and said wire 72 is soldered orotherwise connected with the plate 56. This wire provides a groundingconnection for the motor supporting strap 48 and for the casing of themotor 44.

It will be apparent that motors dilfering in exterior size from thedisclosed motor 44 can be readily accommodated by merely substituting astrap similar to the strap 48 but differing in size to accommodate theselected motor. The strap 48 can be smaller than that shown, and thespace between the strap 48 and the periphery of the opening 42 permitslarger straps to be substituted without any necessary change in thepartition.

Secured to at least one projecting end portion of the motor shaft is arotary air impeller with the shroud at the corresponding intake opening.When there are two side walls and two intake openings, the projectingend portions 46, 46 of the motor shaft carry two rotary air impellersrespectively indicated at 74 and 76. The impellers are providedrespectively with blades 78, 80 and 82, 84 uniformly spacedcircumaxially. The outer portions of the blades of the two impellers arerespectively within the shrouds 28 and 30, and said portions at theirperipheral edges have reasonable running clearances with respect to theshrouds. Otherwise stated, the radii of said outer portions of theblades are only slightly less than the internal shroud radius. The twoimpellers 74 and 76 are shown in Fig. 2 as being identical in size andshape except for opposite pitches of their said blades. The impellers 74and 76 rotate in the clockwise direction as viewed in Fig. l, and theblades 78, 80 and 82, 84 have opposite pitches so that they draw air inopposite directions and inwardly through the corresponding shrouds andintake openings and toward the motor 44 and toward the panel orpartition 36.

Preferably and as shown, the two impellers 74 and 76 have the samenumber of blades and said blades of the two impellers are incircumaxially staggered relationship with each other as shown in Figs. 1and 2. This staggered relationship substantially reduces noise.

The invention is not necessarily limited as to all of the details ofimpeller construction, but it is important that the total or aggregatewidth of all of the blades of each impeller be relatively large with acorresponding relatively large total or aggregate blade area. In orderto provide the required total blade width each impeller preferablycomprises two separate sheet metal blade members as illustrated in Fig.4, the blade members for the front impeller 74 being shown. Said blademembers have circular central portions 86 and 88 and said centralportions are in engagement. As shown, the central portion 86 of theblade member which is at the front has the blades 78 formed integrallytherewith and the central portion 88 of the blade member which is at therear has the blades 80 formed integrally therewith. Said centralportions 86 and 88 of the two blade members are suitably connected to ahub 90 and said blade members are so located on the hub 90 that saidblades 78 and 88 are in staggered circumaxial relationship with eachother. By providing two separate blade members, the blades 78, 78

and 80, 30 can be much wider than would be possible if there were only asingle blade member. As shown, there are four blades 78 on one blademember and four blades 80 on the other blade member, but the inventionis not limited as to the number of blades.

The hubs 90 of the two impellers are connected by set screws 92 to thecorresponding motor shaft portions 46 so that portions of the impellerblades are within the shrouds as previously stated.

Each of said blades 78, 78 and 80, 80 on the two blade members has anouter leading edge 96 and an inner trailing edge 98 and the two edgesare preferably parallel with each other and with a radial line throughthe center of the blade. Said leading and trailing edges 96 and 98 arerelatively long so as to provide the main section thereof with arelatively large effective area, but, as shown, the bladeis so formedthat the trailing edge 98 is somewhat shorter than the leading edge 96.Each blade is twisted at its root portion 94 to provide a suitable pitchangle as hereinafter more fully explained. Said root portion 94 of eachblade is preferably located near the outer edge thereof, as clearlyshown in Fig. 2, so that the main section of the blade projects oroverhangs inwardly. The said main sections of the blades are suitablycurved as also hereinafter more fully explained. After twisting, theleading edges 96 of all blades are approximately in a planeperpendicular to the central axis, and the trailing edges 98 of allblades are approximately in another plane perpendicular to the centralaxis. Said plane of the leading edges 96 is at least approximatelycoincident with the plane of the corresponding side wall, and said planeof the trailing edges 98 is near the panel or partition 36. As shown,all portions of the outer or peripheral edges of the aforesaid mainsections of the blades are equidistant from the axis 12, but this is notalways essential as will be hereinafter explained. Preferably, theblades 78, 78 and 80, 80 are so related to their corresponding centralportions 86 and 88 that said blades have registering rotative paths.Figs. 1 and 2 of the drawings show a blower unit wherein the housing hastwo opposite intake openings and wherein a single motor supports anddrives two impellers respectively adjacent said intake openings.However, the invention is not limited to a two-impeller unit and as tocertain aspects it comprehends aunit having only one impeller. Fig. 4shows a unit having only one impeller, this unit being identical inconstruction with the left portion of the two-impeller unit shown inFig. 2. In view of the identityof construction no detailed separatedescription is necessary as to the alternative unit.

The presently preferred shape and pitch of each blade and therelationship of the blade to other parts are illustrated in Fig. 4 andin the schematic Fig. 5. Fig. 5 is applicable to the two-impeller unitas shown in Figs. 1 to 4 and is also applicable to the single-impellerunit as shown in Fig. 4

Each blade is transversely curved, preferably circularly, to provide aconcave face at the leading or pressure side. of the curve thereof asrepresented by a in Fig. 5 is from to 20% of the length of the bladechord represented by b. The optimum camber a may be about of b.

The mean pitch angle of each blade with respect to a plane parallel tothe axis as represented at c is within the range of 45 to 60, and theoptimum mean pitch angle may be about 50. The blade curvature and theblade pitch angle are such that a tangent to the curvature at thetrailing edge is approximately perpendicular to the panel 36 andapproximately parallel with the axis 12.

As has been stated, it is important to provide a large aggregate bladewidth for each impeller and therefore a large aggregate blade area. Witha large pitch angle such as above stated, the axially projected width ofeach blade is much less than the actual width measured along thecurvature of the blade, but even so the axially projected width islarge. The axially projected width of each impeller blade at orapproximately at the periphery of the blade portion within thecorresponding shroud is indicated at d in Fig. l. The aggregate of theaxially projected widths of all of the blades at or approximately at theperipheries is 50% or more of the circumference of a circle includingsaid peripheries. The required width and area of each blade are afunction of the number of blades, and it will be obvious that, for anychosen aggregate blade width and area, the width. and area per bladewould decrease proportionately to an increase in the number of blades.

When the pitch angle is within the range of 45 to 60 and when theaggregate of the axially projected blade Widths is 50% or more of thecircumference of a corresponding circle as above stated, it will beevident that the aggregate of the actual widths measured along thecurvature of the blades is on the order of 100% of the correspondingcircle.

It is important that the blades of each impeller be properly locatedaxially with respect to the corresponding shroud. In Fig. 5 the line erepresents the plane of the inner edge of the shroud 28, the line frepresents the plane of the outer edge of the cylindricalportion of theshroud, the line g represents the plane of the housing side wall, andthe line It represents the plane of the inner edges of the impellerblades. The outer edges of the blades are shown as being at said line grepresenting the plane of the housing side wall. The dimension i betweenthe lines g and h is the total laterally projected depth of the blades,that is, the depth projected in the direction of rotation or on a radialplane through the axis 12. Stated otherwise, the dimension i is thedistance between'the plane of rotation of the leading edges of theblades and the plane of rotation of the trailing edges of the blades.The dimension j between the lines 2 and h is the laterally The blade isso curved that the depth or camber projected depth of the exposed orprotruding portion of i the blades that extends axially inwardly beyondthe end of the corresponding shroud at e. Said dimension i should bewithin the range of 60% to of said dimension i representing the totalprojected depth of the blades; The dimension k between the lines 1 and eis the total Said dimension I should be at least 30% of the dimension 1'which is the total laterally projected depth of the blades. The shroudmay also project outwardly from the housing and the dimension k maytherefore be larger than the dimension 1, but this is not essential.

The projected depth of the main section of each blade is such that thetrailing portion of said main. section overlies the motor 44 to asubstantial extent and moves around said motor, the trailing inner edges98 of the blades being in a plane between the partition 36 and the endof the motor casing. This conserves space and makes it possible for theoverall width of the unit to be substantially less than .would otherwisebe necessary. Furthermore, the said location of the trailing portions100 of the blades improves air circulation around the motor so that themotor is more effectively cooled. In order to further conserve space andto provide a minimum overall width of the blower unit, the portions 100of the blades extend axially inwardly so that the trailing edges 98 ofthe blades are relatively close to the second wall or partition 36.

Referring again to Fig. 5, the line m represents the edge of the motorcasing, and the dimension n represents the projection or overhang of theblades with respect to the motor. Said dimension it varies substantiallywith the length of the selected motor, but it is shown as being about35% of the dimension i which is the total projected depth of the blades.The dimension 0 represents the width of the housing between the sidewall 16 andthe second wall or partition 36. The dimension p' is thespacing between the plane of the inner or trailing edges 98 of theblades and the second wall or partition 36 and said dimension p shouldbe as small as reasonably possible. Said dimension p is shown as beingabout 7% of the dimension 0.

It will be apparent from the drawings and from the foregoingdescription, that the air as moved by the blades of 'each impeller hasthree directional components of movement.

tangentially in the direction of impeller rotation. The portion of theprojected blade depth which the air initially engages is located withinthe corresponding shroud as previously stated, and therefore the initialair movement has little or no radially outward component. In the portionof the projected blade depth that extends radially inwardly beyond theshroud, the air continues'to move axially, such movement being limitedby the partition 36, and in the last said portion of the blade depth,the air also moves radially outwardly. The radially outward component ofthe air movement is the resultof centrifugal action and pressure isdeveloped in the air as discharged from the tips of the blades. Thespace in each chamber within the housing and around the correspondingimpeller is entirely unobstructed and said air under pressure isdelivered into said surrounding space. The corresponding shroud projectsinto me chamber and,

therefore, the space in the outer portion of the chamber duplex, therebeing two chambers in the housing at oppo;

site sides of a central partition each of which chambers has an intakeopening and a shroud, and there being'two Said air moves axially towardthe partition 36, said air moves radially outwardly, and said air movesimpellers respectively in the chambers and located respectively at theintake openings. While a duplex unit may ordinarily be preferred, it isto be understood that the invention, as to some aspects thereof, is notso limited.

Figs. 6 and 7 show an alternative construction which is or may be likethat shown in Figs. 1 to 5, except that there are different impellers 74and 76 wherein the portions of the blades 78*, 80 82 and 84 that extendaxially inwardly beyond the shrouds have projections 102 that extendradially outwardly beyond the radius of the shrouds. The blades at theprojections 102 have a substantially greater radius, and this increasesthe effective areas of the blades.

To facilitate assembly of the unit as shown in Fig. 6, the side walls 16and 18 have openings therein large enough to receive the largerimpellers. The circular angle rings 32 and 34 are larger and are of suchsize as to engage the side walls beyond said openings. Instead of beingwelded in place, the rings 32 and 34 may be fastened by screws 164. Thusthe shrouds 28 and 30 can be assembled and attached after the impellersare in place.

Figs. 8 and 9 show another alternative construction which is or may besimilar to that shown in Figs. 1 to 5, except that there are impellers74 and 76 having different diameters with shrouds 28 and 30 havingcorrespondingly different diameters. As shown, the front impeller 7 thasa diameter substantially smaller than that of the rear impeller 76. Thesmaller impeller blades are represented at 78 80 and the larger impellerblades are represented at 82 84 In the construction shown in Figs. 8 and9, the two impellers have different capacities, and the partition 36need not be exactly midway between the side walls. This unit isparticularly useful when there are two bodies of air which must behandled separately. In this case, two separate discharge ducts, notshown, would be connected to the discharge outlet at 24, the dividingwall between the ducts being extended to engage the partition 36 at theedge 40. When there are two separate bodies of air, they may be atdifferent pressures and it may be desirable to prevent any flow throughthe central opening 42 in the partition 36. To this end a sealing ring106 of flexible material, as shown in Fig. 9, may be attached to themotor supporting strap 4'5 and may be held in engagement with thepartition 36. This ring is not attached to the partition and thereforedoes not affect the resilient mounting of the motor 44.

According to present practice, blower units for small domesticappliances and for such appliances as warm air furnaces and package airconditioners ordinarily comprise centrifugal blower wheels havingforwardly curved blades. The performance of a blower unit of this typeis graphically presented by the dotted curves of the chart in Fig. 10,it being assumed that the impellers are rotated at a constant speed of1000 rpm. The curve A shows the relationship between the pressuredeveloped by the blower unit and the volume of air that it can move orthe air flow, and the curve B shows the relationship between the volumeof air flow and the necessary brake horsepower. It will be understoodthat said curves A and B are inr tended to be merely illustrative andnot to accurately represent any actual application.

It is normal practice to design the blower unit to provide a chosen airflow at a chosen pressure with the motor operating under normalconditions. in the illustrated example, the chosen air flow is about 260c.f.m. and the chosen pressure is about .44 inch as represented by thepoint C on curve A. This point C corresponds to a brake horsepoweroutput of about .037 as represented by the point D on curve B. The saidbrake horsepower is well within the normal operating range of theselected motor.

In many installations, as in a warm air furnace system for example,situations may arise by the opening of dampers or otherwise wherein theair flow is increased is no overloading.

far beyond the normal air flow for which the unit was designed. Forinstance, the air flow may be increased to that represented by the pointE, that is, about 420 c.f.m. The said increase in air flow requires anincrease in brake horsepower to that represented by the point F on curveB, or about .063 horsepower. This increase in brake horsepower greatlyoverloads the motor and may result in serious damage thereto ifcontinued. Obviously, the degrees of motor overloading would be evenmore serious with a greater increase in air flow.

In a blower unit embodying the present invention, whether as shown inFigs. 1 to 5 or in Figs. 6 and 7 or in Figs. 8 and 9, the describedshapes of the impeller blades and the relationship of the blades withother parts serve to eliminate, or to at least greatly reduce, theabovedescribed limitations inherent in blower units as heretoforeprovided. Assuming that the same motor is selected, the full line curvesA and B correspond respectively to the previously described dotted linecurves A and B. It should be particularly observed that curve B isalmost fiat and varies only slighty from a straight line and that itrepresents only relatively small increases in brake horsepower forincreases in air flow. It is assumed that the blower unit embodying theinvention was designed for the same chosen air flow, and the point C istherefore common to curves A and A. The brake horsepower is thatrepresented by the point D which is common to the curves B and B.

if the air flow is increased to the same extent as before, that is, tothat represented by the point B on curve A, the increase in brakehorsepower is only to that represented by the point P on the curve B,that is, about .045. The slightly increased brake horsepower is wellwithin the normal operating range of the motor and there Even with anadditional opening of dampers and with a much greater increase in airflow, there would be no abnormal increase in loading. As illustrated bycurves A and B, the increase in horsepower is only about 55% when theair flow is increased from about 10G c.f.m. to about 500' c.f.m.

A blower unit embodying the invention eliminates overloading of themotor as above described. Furthermore, it is possible to use a unit fora variety of installations having widely different air-flowrequirements. For example, the unit as above described could be used,without motor overloading, for various air flow requirements rangingfrom perhaps c.f.m. to perhaps 500 c.f.m. This greatly facilitatesmanufacture and sale as only a very few different sizes and designs ofunits would be needed for all requirements of customers. A blower unitembodying the invention has the further advantage that it is smaller andless expensive than prior units of comparable capacity.

The invention claimed is:

1. In a blower unit, the combination of a housing including a front sidewall having a circular intake opening concentric with a central axis andincluding a second wall behind said front wall and parallel therewith,said housing having a peripheral discharge opening and having a chambertherein which is substantially closed except for said intake anddischarge openings and which is unobstructed except for some of thehereinafter stated parts, a cylindrical shroud fitted within said intakeopening, an electric motor including a drive shaft, means for supportingsaid motor with its drive shaft concentric with said central axis andwith a portion of said shaft projecting toward the plane of said frontwall, and an air impeller comprising a hub and a plurality of uniformlyspaced blades connected with said hub and extending generally radiallytherefrom which hub is secured to the projecting portion of said motorshaft and is so located that the outer portions of its blades are withinsaid shroud, said outer portions of the blades of the impeller havingradii only slightly less than the internal shroud radius and said bladesin their entireties being so pitched that said impeller amt-as V 9 r a ri 7 serves upon rotation by the motor to draw air inwardly through theshroud and intake opening and each blade of said impeller having a meanpitch angle with respect to a plane parallel to said axis which iswithin the range of 45 to 60 and each blade of said impeller having aportion of its laterally projected depth extending axially inwardlybeyond the shroud to an extent Within the range of 60% to 70% of thetotal laterally projected depth.

2. A blower unit asset forth in claim 1, wherein each blade of theimpeller is transversely curved to provide a concave face at the leadingor pressure side and is so curved that the camber of its curve is withinthe range of 10% to of the length of the blade chord.

3. A blower unit as set forth in claim 1, wherein a portion of theshroud extends inwardly from the front side wall andtwherein the lengthof the last said portion of the shroud is at least of said totallaterally projected depth of the blades of the impeller.

4. A blower unit as set forth in claim 1, wherein said electric motorincludes a casing which is located at least partly within the housingchamber and wherein each blade of the impeller has a substantial portionof its laterally projected depth extending axially inwardly beyond theouter end of the motor casing and rotatable around the portion of saidmotor casing which is within the chamber.

5. In a blower unit, the combination of a housing including parallelside Walls respectively having circular intake openings concentric witha common central axis which housing has a peripheral discharge openingandis closed except for said intake and discharge openings, a thinpartition in said housing parallel with and midway between said sidewalls and having a generally circular opening concentric with said axis,said partition providing two equal chambers within the housing whichchambers are completely separated except for said partition opening andwhich chambers are unobstructed except for some of the hereinafterstated parts, two cylindrical shrouds respectively fitted within saidintake openings, an electric motor including a casing and including adrive shaft having portions projecting at both ends of the casing,means'for supporting said motor on. said partition with the casingsymmetrically located in said partition opening and with said shaftportions concentric with said central axis and projecting toward theplanes of said side walls, and two air impellers each comprising a huband a plurality of uniformly spaced blades connected with said hub andextending generally radially therefrom which hubs of the two impellersare secured respectively to the projecting portions of said motor shaftand are so located that the outer portions of the blades are within thecorresponding shrouds, said outer portions of the blades of the twoimpellers having radii only slightly less than the internal radii of theshrouds and said blades of the two impellers in their entireties havingopposite pitches so that each impeller serves upon rotation by the motorto draw air inwardly through the corresponding shroud and intake openingand each blade of each impeller having a mean pitch angle with respectto a plane parallel to said axis which is within the range of and andeach blade of each impeller having a portion of its laterally projecteddepth extending axially inwardly beyond the corresponding shroud to anextent within the range of 60% to 70% of the total laterally projecteddepth.

6. A blower unit as set forth in claim 5, wherein the two impellers havethe same number of blades, and wherein the uniformly spaced blades ofthe two impellers are in circumaxially staggered relationship with eachother.

7. In a blower unit, the combination of a housing including a front sidewall having a circular intake opening concentric with a central axis andincluding a second wall behind said front wall and parallel therewith,said housing having a peripheral discharge opening and having a chambertherein which is substantially closed except for said intake anddischarge openings and which is un u 1G,,r obstructed exceptfor thehereinafter stated parts, a cylindrical shroud fitted within said intakeopening, anlelectric motor including a drive shaft, means for supportingsaid motor'within its drive shaft concentric with said central axis andwith a portion of said shaft projecting toward the plane of said frontwall, and an airlimpeller comprising a hub and a plurality of generallyradial uniformly spaced blades connected with said hub and extendinggenerally radially therefrom which hub is secured to the projectingportion of said motor shaft and is so located that the outer portions ofthe blades are within said shroud, said outer portions of the blades ofthe impeller having radii only slightly less than the internal shroudradius and said blades in their entireties being so pitched that saidimpeller serves upon rotation by the motor to draw air inwardly throughthe shroud and intake opening and each blade of said impeller having amean pitch angle with respect to a plane parallel to said axis which iswithin the range of 45 to 60 and the blades of said propeller being ofsuch laterally projected depths and so located that their outer leadingedges are approximately in the plane of said front wall and that theirinner trailing edges are close to said second wall so that the width ofthe housing between saidrfront wall and said second wall is onlyslightly greater thanthe total laterally projected depths of the bladesof the impeller.

8. In a blower unit, the. combination of a housing including parallelside walls respectively having circular intake openings concentric witha common central axis which housing has a peripheral discharge openingand is closedexcept for said intake and discharge openings, a thinpartition in said housing parallel with and midway between said sidewalls and having a generally circular opening concentric with said axis,said partition providing two equal chambers withinthe housing, whichchambers are completely separated except for said partition opening andwhich chambers are unobstructed except for the hereinafter stated parts,two cylindrical shrouds respectively fitted within said intake openings,an electric motor including a casing and including a drive shaft havingportions projecting at both ends of the casing, means for supportingsaid motor on said partition with the casing symmetrically located insaid partition opening and with said shaft portions concentric with saidcentral axis and projecting toward the planes of said side walls, andtwo air impellers each comprising a hub and a plurality of uniformlyspaced blades connected with said hub and extending generally radiallytherefrom which hubs of the two impellers are secured respectively tothe projecting portions of said motor shaft and are so located that theouter portions of the blades are within the corresponding shrouds, saidouter portions of the blades of the two impellers having radii onlyslightly less than the internal radii of the shrouds and said blades ofthe two impellers in their entireties having opposite pitches so thateach impeller serves upon rotation bythe motor to draw air inwardlythrough the corresponding shroud and intake opening and each blade ofeach impeller having a mean pitch angle with respect to a plane parallelto said. axis which is vw'thin the range of 45 to 60 and the blades ofeach propeller being of such laterally projected depths and so locatedthat their outer leading edges are approximately in the plane of thecorresponding side wall and that their inner trailing edges are close tothe central partition so that the total width of the housing is only,slightly greater than the, total of the laterally projected cylindricalshroud fitted within said intake opening, an electric motor including adrive shaft, means for supporting said motor with its drive shaftconcentric with said central axis and with a portion of said shaftprojecting toward the plane of said front wall, and an air impellercomprising a hub and a plurality of generally radial uniformly spacedblades connected with said hub and extending generally radiallytherefrom which hub is secured to the projecting portion of said motorshaft and is so located that the outer portions of the blades are withinsaid shroud, said outer portions of the blades of the impeller havingradii only slightly less than the internal shroud radius and said bladesin their entireties being so pitched that said impeller serves uponrotation by the motor to draw air inwardly through the shroud and intakeopening and each blade of said impeller having a mean pitch angle withrespect to a plane parallel to said axis which is within the range of 45to 60 and the aggregate of the axially projected widths of all of theblades of said impeller approximately at the periphery of the portionwithin the shroud being at least 50% of the circumference of a circleincluding said periphery.

10. A blower unit as set forth in claim 9, wherein each blade of thepropeller has a portion extending radially inwardly beyond the shroudwhich last said portion has a laterally projected depth which is withinthe range of 60% to 70% of the total laterally projected depth.

11. A blower unit as set forth in claim 9, wherein the impeller includestwo separate blade members each provided with one-half of the bladeswhich members have central portions in engagement with each other andconnected to the hub and are so relatively positioned that all of theblades are uniformly spaced circurnaxially.

12. A blower unit as set forth in claim 11, wherein said electric motorincludes a casing which is located at least partly within the housingchamber, wherein each blade is connected with the central portions ofthe corresponding blade member by a narrow neck located near one side ofthe blade, and wherein said neck has been twisted relatively to saidcentral portion to provide the required mean pitch angle and to positionthe trailing portion of the blade and the trailing edge thereof axiallyinwardly beyond the portion of said motor casing which is within thechamber,

13. A blower unit as set forth in claim 12, wherein the blades of theimpeller are of such width and so located that their outer leading edgesare approximately in the plane of the front side wall and that theirinner trailing edges are close to the second wall so that the totalwidth of the housing is only slightly greater than the total of theprojected depths of the blades of the two impellers.

14. In a blower unit, the combination of a housing including parallelside walls respectively having circular intake openings concentric witha common central axis which housing has a peripheral discharge openingand is closed except for said intake and discharge openings, a thinpartition in said housing parallel with and midway between said sidewalls and having a generally circular opening concentric with said axis,said partition providing two equal chambers within the housing whichchambers are completely separated except for said partition opening andwhich chambers are unobstructed except for the hereinafter stated parts,two cylindrical shrouds respectively fitted within said intake openings,an electric motor including a casing and including a drive shaft havingportions projecting at both ends of the casing, means for supportingsaid motor on said partition with the casing symmetrically located insaid partition opening and with said shaft portions concentric with saidcentral axis and projecting towardthe planes of said side walls, and twoair impellers each comprising a hub and a plurality of uniformly spacedblades connected with said hub and extending generally radiallytherefrom which hubs of the two impellers are secured respectively tothe projecting portions of said motor shaft and are so located that theouter portions of the blades are within the corresponding shrouds, saidouter portions of the blades of the two impellers having radii onlyslightly less than the internal radii of the shrouds and said blades ofthe two impellers in their entireties having opposite pitches so thateach impeller serves upon rotation by the motor to draw air inwardlythrough the corresponding shroud and intake opening and each blade ofeach impeller having a mean pitch angle with respect to a plane parallelto said axis which is within the range of to 60 and the aggregate of theaxially projected widths of all of the blades of each impellerapproximately at the peripheries of the portions within the shroudsbeing at least of the circumference of a circle including saidperipheries.

15. A blower unit as set forth in claim 14, wherein each blade of eachpropeller has a portion extending axially inwardly beyond thecorresponding shroud which last said portion is within the range of toof the total projected depth.

16. A blower unit as set forth in claim 14, wherein each impellerincludes two separate blade members each provided with one-half of theblades which members have central portions in engagement with each otherand connected to the corresponding hub and are so relatively positionedthat all of the blades are uniformly spaced circumaxially, wherein eachblade is connected with the central portions of the corresponding blademember by a narrow neck located near one side of the blade, wherein saidneck has been twisted relatively to said central portion to provide therequired mean pitch angle and to position the trailing portion of theblade and the trailing edge thereof axially inwardly beyond thecorresponding outer end of the motor casing, and wherein the blades ofeach impeller are of such width and so located that their outer leadingedges are approximately in the plane of the corresponding side Wall andthat their inner trailing edges are close to the central partition sothat the total width of the housing is only slightly greater than thetotal of the projected depths of the blades of the two impellers.

17. In a blower unit, the combination of a housing including parallelside Walls respectively having circular intake openings concentric witha common central axis which housing has a peripheral discharge openingand is closed except for said intake and discharge openings, a thinpartition in said housing parallel with and midway between said sidewalls and having a generally circular opening concentric with said axis,said partition providing two equal chambers within the housing whichchambers are completely separated except for said partition opening andwhich chambers are unobstructed except for the hereinafter stated parts,two cylindrical shrouds respectively fitted within said intake openings,an electric motor including a casing and including a drive shaft havingportions projecting at both ends of the casing, means for supportingsaid motor on said partition with the casing symmetrically located insaid partition opening and with said shaft portions concentric with saidcentral axis and projecting toward the planes of said side walls, andtwo air impellers each comprising a hub-and a plurality of uniformlyspaced blades connected with said hub and extending generally radiallytherefrom which hubs of the two impellers are secured respectively tothe projecting portions of said motor shaft and are so located that theouter portions of the blades are within the corresponding shrouds, saidouter portion of the blades of the two impellers having radii onlyslightly less than the internal radii of the shrouds and said blades ofthe two impellers in their entireties having opposite pitches so thateach impeller serves upon rotation by the motor to draw air inwardlythrough the corresponding shroud and intake opening and each blade ofeach impeller having a mean pitch angle with respect to a plane parallelto said axis which is within the range of 45 to 60 and a substantialportion of the laterally projected depth of each blade of each 13impeller extending axially inwardly beyond the corresponding shroud andhaving a radius substantially greater than that of the portion withinthe shroud.

18. A blower unit as set forth in claim 17, wherein the laterallyprojected depth of said inwardly extending portion of each blade iswithin the range of 60% to 70% of the total laterally projected depth ofthe blade.

19. A blower unit as set forth in claim 18, wherein each blade of eachimpeller has a substantial portion of its laterally projected depthextending axially inwardly beyond the corresponding outer end of themotor casing and rotatable around said casing.

20. In a blower unit, the combination of a housing including parallelside walls respectively having circular intake openings with differentradii concentric with a common central axis which housing has aperipheral discharge opening and is closed except for said intake anddischarge openings, a thin partition in said housing parallel with andbetween said side walls and having a generally circular openingconcentric with said axis, said partition providing two chambers withinthe housing which chambers are completely separated except for saidpartition opening and which chambers are unobstructed except for thehereinafter stated parts, two cylindrical shrouds with different radiirespectively fitted within said intake openings, an electric motorincluding a casing and including a drive shaft having portionsprojecting at both ends of the casing, means for supporting said motoron said partition with the casing symmetrically located in saidpartition opening and with said shaft portions concentric with saidcentral axis and projecting toward the planes of said side walls, andtwo air impellers each comprising a hub and a plurality of uniformlyspaced blades connected with said hub and extending generally radiallytherefrom and respectively having outer portions with diiferent radiiconforming to the radii of the corresponding shrouds which hubs of thetwo impellers are secured respectively to the projecting portions ofsaid motor shaft and are so i4 located that the said outer portions ofthe blades are within the corresponding shrouds, the blades of the twoimpellers having radii only slightly less than the internal inwardlythrough the corresponding intake opening and' each blade of eachimpeller having a pitch angle with respect to a plane parallel to saidaxis that is within the range of to 21. A blower unit as set forth inclaim 20, wherein the laterally projected depth of said inwardlyextending portion of each blade is within the range of 60% to of thetotal laterally projected depth of the blade.

22. A blower unit as set forth in claim 20, wherein each blade of eachimpeller has a substantial portion of its later-ally projected depthextending axially inwardly beyond the corresponding outer end of themotor casing and rotatable around said casing.

References Cited in the file of this patent UNITED STATES PATENTS267,707 Mills Nov. 21, 1882 1,149,638 Davidson Aug. 10, 1915 1,827,316Haynesworth Oct. 13, 1931 1,843,088 Minnard Jan. 26, 1932 2,011,298Osbun et al Aug. 13, 1935 2,160,667 McMahan May 30, 1939 2,176,325Bretzlaif et al Oct. 12, 1939 2,297,050 Cotton et al. -2 Sept. 29, 19422,316,608 McMahan Apr. 13, 1943 2,325,222 Bretzlafi et a1 July 27, 19432,350,939 Sprouse June 6, 1944 2,354,653 Allen Aug. 1, 1944 2,650,755Woodward Sept. 1, 1953 2,814,432 Eiserman Nov. 26, 1957 2,823,852 BuschFeb. 18, 1958

